The relationship between membrane events and secretion of pituitary hormones needs clarification. The general aim of the proposed research is to study the electrophysiological correlates of corticotropin (ACTH) secretion, and to combine these studies with rapid biochemical studies of the secretion of ACTH. For both electrophsiological and biochemical studies, a mouse pituitary cell line that synthesizes and secretes multiple forms of ACTH will be used. The resting and active membrane properties will be determined for the cells, and the medium used for serum-free growth of the cells will be improved. Simultaneous biochemical and electrophysiological studies will then be performed using a controlled, in vitro system with adequate temporal resolution to match secretory events seen in the whole organism.